The present disclosure generally relates to releasable attachment mechanisms used to fasten, retain, or latch together components of an apparatus or a structure that are to be separated or released under controlled conditions.
Hook and loop fasteners as well as knob and cavity type fasteners are well known and generally used to join two members detachably to each other. These types of fasteners generally have two components disposed on opposing member surfaces. One component typically includes at least one protrusion, i.e., a knob or hook, while the other component typically includes a cavity dimensioned to frictionally fit the knob or a loop of material configured to engage the hooks. When the two components are pressed together they interlock to form a releasable engagement. The resulting joint created by the engagement is relatively resistant to shear and pull forces, and weak in peel strength forces. As such, peeling one component from the other component can be used to separate the components with a minimal applied force. As used herein, the term “shear” refers to an action or stress resulting from applied forces that causes or tends to cause two contiguous parts of a body to slide relatively to each other in a direction parallel to their plane of contact. The term “pull force” refers to an action or stress resulting from applied forces that causes or tends to cause two contiguous parts of a body to move relative to each other in a direction perpendicular to their plane of contact.
The shear and pull off forces for these types of systems are generally limited. For example, the dimensions of current knob and cavity fasteners must be carefully considered to permit both fastening and disengagement. Because the knob portion is force-fit within the cavity to effect engagement, the applied pull-off and shear forces for these fastening systems will be limited to the frictional forces associated with pulling or shearing the knob from the cavity or the force levels required to physically deform the knob sufficiently so that it will fit/exit through the cavity entrance. As such, the various forces to effect disengagement will approximate or even greatly exceed those used for engagement. Hook and loop type systems will be similar although the number of hooks engaged with the loop material will collectively provide relatively higher shear and pull-off forces.
It would be desirable to selectively increase the shear and lift off forces when the fastener system is intended to remain fastened and selectively decrease the shear and lift off forces when effecting disengagement so as to minimize the forces necessary to effect disengagement.